The present invention provides a combustion apparatus for use in a high-temperature environment, such as in a gas turbine, or elsewhere. More particularly, the invention includes a catalytic combustor which one can use as the initial stage in a multi-stage high-temperature combustion apparatus.
The present invention represents an improvement over the product and method described in copending U.S. patent application Ser. No. 07/408,521, filed Sep. 18, 1989, entitled "Combustion Apparatus for High-temperature Environment". This specification hereby incorporates the disclosure of the latter application by reference.
When a fuel-air mixture flows through the channels of a catalytic reactor, the temperature of the mixture increases smoothly as the combustion proceeds. But the temperature of the catalyst-coated wall of the channel does not increase smoothly. Instead, this temperature increases rapidly near the entrance to the channel and approaches the adiabatic combustion temperature. Then it remains close to the adiabatic combustion temperature over the length of the channel.
If one makes the channel too short to achieve complete combustion, the exiting gas will have a temperature below the adiabatic combustion temperature. Even so, the catalyst-coated wall will have a temperature close to adiabatic, over all but the front end of the channel. Thus, even with a shortened catalytic combustion channel, the catalyst-coated walls still reach the adiabatic temperature, thereby deactivating the catalyst.
The above-cited patent application discloses one solution to the above problem. The latter application shows a catalytic reactor made of a single strip of metal coated with catalyst on one side only. One embodiment includes a strip folded back and forth upon itself, in a zigzag pattern, to form a catalytic reactor. In another embodiment, either one or two strips become wound into a spiral. In either case, the catalytic reactor defines channels for gas flow in which a catalyst coats either all or none of each channel.
The present invention provides a modified structure which more evenly distributes the coated and uncoated portions of the metal strip. The invention also includes a method for making a catalytic reactor. The present invention prevents the walls of the combustor from reaching the adiabatic combustion temperature, as compared with catalytic combustors of the prior art.